Estimating the concentration of solid matter suspended in a fluid stream

ABSTRACT

Continuously measuring the concentration of fibre suspended in a liquid stream (such as a flow of pulp to a papermaking machine) by placing in the stream a mesh screen of such mesh size as catches fibre but not smaller suspended matter, rotating the screen about an axis in its own plane and at right angles to the direction of flow so that catches of fibre are successively made by the screen and washed off it by the flow, and measuring the amplitude of the fluctuation of pressure difference between upstream and downstream of the rotating screen due to the obturating effect of the fibre &#39;&#39;&#39;&#39;catch.

Williams 1 July 8, 1975 [5 ESTIMATING THE CONCENTRATION OF 3,086,905 4/1963 Richardson 73/63 X D T ER U PENDED [N A FLUID 3,110,172 11/1963 Irwin i i v 73/54 SOL MA T S S 3,359,786 12/1967 Von Alfthan 73/61 R STREAM [75] Inventor: David Joseph Williams, East FOREIGN PATENTS 0R APPLICATIONS Ivanhoe, Australia 136,267 8/1960 U.S.S.R .7 73/61 R [73] Assignee: A ustralian Paper Manufactures Primary Examiner Richard C Queisser South Melbourne Assistant Examiner-Joseph W. Roskos Austraha Attorney, Agent, or Firm-Ladas, Parry, Von Gehr, 221 Filed: Jan. 16, 1974 Goldsmith & Deschamps App]. No.: 433,934

Foreign Application Priority Data Jan. 24, 1973 Australia 1. 2010/73 U.S. Cl. 73/61 R; 73/63 Int. CL. G01N 15/06 Field of Search 73/61 R, 63, 54; 137/4,

References Cited UNITED STATES PATENTS 3/1958 Forsten et al 73/63 10/1962 Read et 73/61 R [57] ABSTRACT Continuously measuring the concentration of fibre suspended in a liquid stream (such as a flow of pulp to a papermaking machine) by placing in the stream a mesh screen of such mesh size as catches fibre but not smaller suspended matter, rotating the screen about an axis in its own plane and at right angles to the direction of flow so that catches of fibre are successively made by the screen and washed off it by the flow, and measuring the amplitude of the fluctuation of pressure difference between upstream and downstream of the rotating screen due to the obturating effect of the fibre catch.

1 ESTIMATING THE CONCENTRATION OF SOLID MATTER SUSPENDED IN A FLUID STREAM This invention relates to the continuous estimation or measurement of the concentration of fibre or other relatively large solid matter suspended in a fluid stream.

In the papermaking art in particular it is often important or at least desirable to have such a measurement, be it to monitor the efficiency of fibre recovery to avoid undue loss, or to ensure that fibre concentrations in effluents remain within specified disposal concentration limits.

Known methods have usually been gravimetric" (generally batchwise and mostly unadaptable or inconvenient for continuous monitoring) or turbidimetric," measuring the optical density of the suspension (but this is often incapable of discriminating fibrous from other suspended matter such as clay).

An object of this invention is to provide a simple method and apparatus for continuously estimating the concentration of fibre or other large solid matter suspended in a uniform fluid stream.

But in order that the invention may be better understood, reference will now be made to the accompanying drawing which is to be considered as part of this specification and read herewith.

The single drawing is a diagram of a preferred form of apparatus according to the invention for measuring on a continuous or substantially continuous basis the concentration of fibre suspended in a fluid stream. Part of the stream is by-passed through pipe I into a constant-head device 2 wherein overflow from weir 3 is discharged to waste through pipes 4 and 5.

The fluid suspension passes from the upstream" side of weir 3 into the lower end of a long, preferably vertical cylindrical chamber 6 designed to encourage a uniform flow of fluid therein which is educed through the upper end of the chamber into a second constant head device 7 from which overflow passes to waste through pipe 5. It will be seen that devices 2 and 7 afford a constant pressure head (represented by the difference in their upstream levels) for the flow in chamber 6.

About mid-height in the chamber is a screen or sieve 8 of shape similar to the cross-section of the chamber but slightly smaller so as to be rotatable therein about an axis in its plane and transverse to the chamber. For this purpose the sieve is fitted with a shaft 9 passing through a suitable gland in the side wall of the chamber and is rotated at about two rotations per minute by motor 10. The pressure difference between upstream and downstream of the sieve is sensed by manometer means e.g. a manometer, or a differential pressure transmitter or appropriate sensitivity. Advantageously pressure-tappings in the form of pipes II, 12 lead respectively from the upstream and downstream sides of the sieve so as to be clear of its region of movement. Pipes 1] and I2 respectively lead into the lower ends of open-tube manometers 13, I4 which may be flushed to waste, as needed, through valves 15, 16.

The mesh size of screen 8 is carefully chosen so as to catch fibres, but allow substantially unimpeded passage of the fluid and any small suspended particles. Then as the screen assumes a suitable position in the stream, the obturating effect of the fibre enmeshed therein will impose a pressure. difference (AP) which at any time is substantially reflected in the difference of levels between 13 and 14. Thus if the screen were suddenly introduced transversely into the chamber and kept in that position, AP would increase from approximately zero and would, in time, asymptotically approach a maximum value. Evidently the rate of increase would be a measure of the fibre concentration.

However, a more convenient measurement is made by continuously rotating the screen as shown in the drawing. Let it be assumed that the operation commence with the screen substantially parallel to the flow and hence AP substantially zero. As the screen is turned, it begins to strain out solids which increasingly obturate the screen and give rise to the pressure difference AP. The solids thus enmeshed will be washed away as the screen rotates over the second quadrant of its motion, and a fresh catch will similarly be made and released during the ensuing and subsequent half-cycles, during each of which it will be apparent AP will increase from substantially zero to a maximum and then decrease to the initial (substantially zero) value. AP therefore oscillates at twice the frequency of rotation of the screen, and for a particular screen, the amplitude of the oscillation of AP will be a function of the fibre concentration, the velocity of the stream and the angular velocity of rotation of the screen.

The mesh size will need to be carefully chosen. If too large, it will pass all solids and AP will remain substantially zero, no matter how slowly the screen should turn. If the mesh be too small it will catch undesirably small particles and AP will not afford a reliable indication of fibre as distinct from total solids concentration.

Likewise the rotational speed of the screen must be suitably adjusted. If too rapid, insufficient fibre will be caught and any AP will probably be due to extraneous turbulence imposed on the stream by the screens rotation. If too slow, the effect of accumulated fibre will be that of a small-mesh screen which will tend also to catch smaller particles once an initial mat of fibre has deposited, leading to a complete obturation of the screen. The maximum AP (i.e. the amplitude of the AP oscillation curve) thus obtained would therefore reflect the effect of a solid barrier in the stream rather than the effect of fibre accumulation on the screen.

It will be evident from the foregoing that the present invention provides a relatively simple arrangement for estimating or measuring the fibre concentration on a continuous basis, and wherein the fibre is suitably discriminated from small particles. It will further be apparent that the mesh is self cleaning and that the system is unaffected by colour changes in the effluent and similar problems that affect optical systems.

Having now described our invention, what we claim as new and desire to secure by letters patent is:

1. Apparatus for carrying out a method of estimating the concentration of large solids suspended in a fluid stream also containing small-grain solids, comprising a cylindrical flow-chamber, a conduit for continuously removing part of the fluid stream for measurement, a first constant-head device for supplying at least some of said part to one end of the chamber, a second constanthead device for removing fluid from the other end of the chamber, a sieve movable in an intermediate part of the chamber so as selectively to catch solids from the substantially uniform flow that is due to a pressure drop between the constant-head devices, manometer means for continuously sensing the pressure difference between upstream and downstream of the sieve, and

means for deriving therefrom a measure of the relevant solids concentration.

2. Apparatus as claimed in claim 1 wherein the sieve is of substantially the same form as the crosssection of the chamber, means being provided for uniformly rotating the sieve about an axis in its plane and substantially at right angles to the axis of the chamber.

3. Apparatus according to claim 2 characterized in that the axis of the chamber is vertical and the flow therein is upwards, the first and second constant-head devices being respectively above and below the top and bottom ends of the chamber.

4. Apparatus according to claim 1 wherein the manometer means comprise open-tube manometers placed side-by-side to enable the relevant concentration to be conveniently read-off by direct observation of the maximum difference in levels over a cycle of the sieve.

S. A method of estimating the concentration of solids suspended in a fluid stream comprising the steps of providing a flat sieve of such mesh size as will catch said solid matter but allow substantially unimpeded passage of the fluid and small suspended matter therethrough, rotating the sieve about an axis in its plane and substantially perpendicular to the direction of flow of the stream to bring the sieve into a position transverse to the stream, and sensing the rate of increase of pressure drop between upstream and downstream of the sieve.

6. A method of estimating the concentration of solids suspended in a fluid stream comprising the steps of providing a flat sieve of such mesh size as will catch said solid matter but allow substantially unimpeded passage of the fluid and small suspended matter therethrough, rotating the sieve about an axis in its plane and substantially perpendicular to the direction of flow of the stream thereby to move the sieve in a regular and periodic manner to and from a position transverse to the stream. and sensing the amplitude of a correspondingly fluctuating pressure differential between upstream and downstream of the sieve.

7. A method of estimating the concentration of large solids suspended in a fluid stream also carrying smallgrain solids, comprising the steps of interposing a flat mesh screen which is rotatable about an axis in its plane and substantially perpendicular to the direction of flow of the stream, rotating the screen about said axis so as to move the screen in a regular and periodic manner into and out of a position in which it selectively catches large solids, thereby to impose a correspondingly regular and periodic varying pressure differential of substantially constant amplitude between two parts of the stream, and utilizing the effect of said pressure differential to estimate concentration of large solids as a function of said amplitude. 

1. Apparatus for carrying out a method of estimating the concentration of large solids suspended in a fluid stream also containing small-grain solids, comprising a cylindrical flowchamber, a conduit for continuously removing part of the fluid stream for measurement, a first constant-head device for supplying at least some of said part to one end of the chamber, a second constant-head device for removing fluid from thE other end of the chamber, a sieve movable in an intermediate part of the chamber so as selectively to catch solids from the substantially uniform flow that is due to a pressure drop between the constanthead devices, manometer means for continuously sensing the pressure difference between upstream and downstream of the sieve, and means for deriving therefrom a measure of the relevant solids concentration.
 2. Apparatus as claimed in claim 1 wherein the sieve is of substantially the same form as the crosssection of the chamber, means being provided for uniformly rotating the sieve about an axis in its plane and substantially at right angles to the axis of the chamber.
 3. Apparatus according to claim 2 characterized in that the axis of the chamber is vertical and the flow therein is upwards, the first and second constant-head devices being respectively above and below the top and bottom ends of the chamber.
 4. Apparatus according to claim 1 wherein the manometer means comprise open-tube manometers placed side-by-side to enable the relevant concentration to be conveniently read-off by direct observation of the maximum difference in levels over a cycle of the sieve.
 5. A method of estimating the concentration of solids suspended in a fluid stream comprising the steps of providing a flat sieve of such mesh size as will catch said solid matter but allow substantially unimpeded passage of the fluid and small suspended matter therethrough, rotating the sieve about an axis in its plane and substantially perpendicular to the direction of flow of the stream to bring the sieve into a position transverse to the stream, and sensing the rate of increase of pressure drop between upstream and downstream of the sieve.
 6. A method of estimating the concentration of solids suspended in a fluid stream comprising the steps of providing a flat sieve of such mesh size as will catch said solid matter but allow substantially unimpeded passage of the fluid and small suspended matter therethrough, rotating the sieve about an axis in its plane and substantially perpendicular to the direction of flow of the stream thereby to move the sieve in a regular and periodic manner to and from a position transverse to the stream, and sensing the amplitude of a correspondingly fluctuating pressure differential between upstream and downstream of the sieve.
 7. A method of estimating the concentration of large solids suspended in a fluid stream also carrying small-grain solids, comprising the steps of interposing a flat mesh screen which is rotatable about an axis in its plane and substantially perpendicular to the direction of flow of the stream, rotating the screen about said axis so as to move the screen in a regular and periodic manner into and out of a position in which it selectively catches large solids, thereby to impose a correspondingly regular and periodic varying pressure differential of substantially constant amplitude between two parts of the stream, and utilizing the effect of said pressure differential to estimate concentration of large solids as a function of said amplitude. 